RTM6 Epoxy Research Articles

Influence of thermoplastic diffusion on morphology gradient and on delamination toughness of RTM-manufactured composites

We explore the influence of the interdiffusion of two thermoplastic tougheners and RTM6 epoxy resin precursors on the resulting morphologies after curing and the consequences on delamination toughness of the corresponding carbon fiber reinforced composites. Two thermoplastics with contrasting Tg and compatibility, i.e. poly(ether sulfone) (PES) and phenoxy are compared. The dramatic improvement of the interlaminar fracture toughness (GIC) found for the phenoxy-RTM6 system as compared to the pure thermoset reference can be ascribed to the broad morphology gradient only observed for that system. By contrast, the PES-RTM6 system is characterized by a steep morphology gradient and a corresponding decrease of as compared to the reference.

High Temperature Nanoindentation Response of RTM6 Epoxy Resin at Different Strain Rates

This paper explores the feasibility of characterizing the mechanical response of the commercial aerospace grade epoxy resin RTM6 by nanoindentation tests at varying temperatures and strain rates. Since glassy polymers exhibit time-dependent mechanical properties, a dynamic nanoindentation technique was used. This method consists on superimposing a small sinusoidal force oscillation on the applied force. Viscoelastic properties are then characterized by their storage and loss moduli, whereas the visco-plastic response of the material can be associated to its hardness. In such experiments, thermal stability of the measuring technique is critical to achieve a low thermal drift and it becomes increasingly important as the measuring temperature increases. Our results show that conventional methods applied for drift correction in nanoindentation of inorganic materials are not applicable to glassy polymers leading to physically inconsistent results. We propose a method for drift correction based on the hypothesis that viscoelastic modulus should be a function of the applied load and frequency but independent of the global strain rate. Using this method, it was possible to determine the viscoplastic properties of RTM6 between RT and 200 °C.

Viscoelastic damping behaviour of cup stacked carbon nanotube modified epoxy nanocomposites with tailored interfacial condition and re-agglomeration

Abstract Re-agglomeration is a natural phenomenon occurring in certain processing methods used in the fabrication of nanocomposites. The work describes the tailoring of the interfacial bonding and morphology in the re-agglomeration of cup stacked carbon nanotubes (CSNTs) modified RTM6 epoxy nanocomposite for potential damping applications. Mechanical and electrical properties were analysed to inform the dispersion and interfacial conditions within the nanocomposites. Samples with resin infused re-agglomerates revealed certain advantages in both mechanical and damping performance. This finding disrupted the traditional compromise between a favourable mechanical property and the energy dissipation of a homogeneously dispersed nanocomposite, allows both properties to be improved under certain interfacial bonding condition. It is proposed that a controlled agglomeration may afford a superior properties combination without sacrificing one another.

Polymerization study and rheological behavior of a RTM6 epoxy resin system during preprocessing step

Curing process and rheological behaviors of a monocomposant epoxy resin used in structural aeronautic applications are investigated. This study helped settle the basic parameters in order to optimize the infusion process of carbon fibers in an epoxy matrix. The effect of carbon nanotube dispersion during the preinjection step is also studied to improve electrical behavior of composite parts. The curing process has been analyzed at isothermal temperature using differential scanning calorimetry technique. Viscosity measurements were achieved with a Couette geometry, suitable for low viscosity resin. A shear-thinning effect caused by adding CNTs in the epoxy matrix is detected. It is more pronounced at high temperature for increasing CNT mass content.

Physical aging of partially crosslinked RTM6 epoxy resin

ABSTRACTThe aging behavior of partially and completely crosslinked RTM6 epoxy resin samples in the glassy state is investigated by thermophysical and mechanical analyses. Curing degree, glass transition temperature, density, and micromechanical modulus are investigated as function of aging period, initial curing degree or depth below the sample surface. A clear increase of density and modulus with aging period as well as an enhanced surface stiffness is detected for all curing degrees. Also, the aging period necessary to achieve the steady state modulus is independent from the curing degree. In contrast, the degree of physical aging induced modulus changes shows a significant dependence on the curing degree. A discontinuity is detected in the so‐called transition region, which is related to the transition from rubber to glassy state during crosslinking. This emphasizes the importance of curing history for physical aging processes and the high potential of partial curing for the development of new processing routes, in particular for production of samples with low sensitivity to physical aging. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41121.

Influence of partial cross‐linking degree on basic physical properties of RTM6 epoxy resin

ABSTRACTThermo‐physical and mechanical properties of partially and completely cross‐linked RTM6 epoxy resin samples in the glassy state have been investigated. A significant dependence of glass transition temperature, density, and modulus on the curing history and the curing degree is found. Density and modulus decrease with increasing curing degree and show a step‐like irregularity in the so called transition region, which is related to the transition from rubber to glassy state during cross‐linking and the starting of structural relaxation processes. The relationship between the thermo‐physical and mechanical properties, which is important for the development of new processing routes for fiber reinforced polymers, is addressed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4338–4346, 2013

Strength of CFRP open hole laminates made from NCF, TFP and braided preforms under cyclic tensile loading

Tensile tests and tension–tension cyclic tests were performed on carbon fibre reinforced plastics open-hole laminates. Specimens made from non-crimp fabric preforms, tailored fibre placement preforms and braided preforms in three different lay-up configurations ([+45]8 s, [+45/0/−45]6 s, [0/90]8 s) were investigated and compared. The laminates were manufactured using a vacuum assisted processing technology and Hexcel RTM6 epoxy resin. Tensile strength and residual tensile strength values were measured and compared with unnotched specimens in order to evaluate the notch sensitivity. To evaluate deterioration during cyclic testing a two-dimensional digital image correlation system was used to capture deformation images of the specimen surface in the open-hole area. Observed similarities and differences in deformation and in load–elongation graphs of the tested specimens are discussed.

An indirect method based on fretting tests to characterize the elastic properties of materials: Application to an epoxy resin RTM6 under variable temperature conditions

An original indirect method of elastic modulus measurement based on fretting tests is developed here. It consists in applying a normal force, then marking the contact area thanks to a tiny cyclic fretting loading. The elastic modulus of the epoxy resin is extrapolated from the post-mortem contact radius measurement using a Hertzian contact description. Applied to a RTM6 epoxy resin, the elastic properties are extracted from this partial slip fretting analysis and are compared to dynamic mechanical analysis data (DMA). Very good agreement was found between these fretting results and data given by DMA analysis, confirming the potential of this new contact method to extract the mechanical properties of materials.

Quantitative control of RTM6 epoxy resin polymerisation by optical index determination

RTM6 epoxy resin curing is usually characterized by the polymerisation degree. We report in this paper on a refractive index measurement technique applied on an experimental mould to control, quantitatively and in situ, the industrial RTM process. For the first time, we determined simultaneously the thermo-optical coefficient, the refractive index evolution, the specific volume and the polymerisation degree of the resin. The calculation of a “polymerisation degree optical coefficient” led to a quantification of the RTM6 epoxy resin polymerisation process. This calibration coefficient is very useful to perform a real time industrial process control. Furthermore, the optoelectronic system is connected to a data processing unit and is easy to use in an industrial environment.

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

AbstractThe cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave‐heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near‐infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy‐amine reaction proceeded more rapidly than did the epoxy‐hydroxyl reaction. This was not the case during conventional curing of this resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3658–3668, 2006